What is the greatest common factor of 48 and 20?

To find the greatest common factor (GCF) of 48 and 20, we can list the factors of each number and then identify the largest factor that they have in common. The factors of 48 are: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48. The factors of 20 are: 1, 2, 4, 5, 10, 20. The common factors of 48 and 20 are: 1, 2, 4. The greatest common factor is the largest of these common factors, which is 4. Therefore, the GCF of 48 and 20 is 4.